"An arm that's going to go into a robot to even drone parts that are going to be flying around," said David Feeney, CEO of SD3D.

It's what they'll take as payment that they can't touch.

SD3D accepts bitcoin; they're not actual coins, but each is a unique piece of computer code that exists in cyberspace.

There's no government or bank involvement. In other words, there are no consumer protections and their value could disappear. But there aren't any of those annoying fees that squeeze customers and businesses.

SD3D's printers can do a lot, but the one thing they can't do is print bitcoin because they don't physically exist.

Bitcoin peaked in popularity in 2013, when one was worth more than $1,100. Now one sells for about $240. They're hard to trace and risky. In fact, detractors say mostly people up to no good use them.

But there are some San Diegans who still see them as the future, bringing power back to the consumer. At a startup called Airbitz in downtown San Diego, founder Paul Puey doesn't pay his 10 workers in dollars.

Airbitz provides a virtual wallet that manages bitcoin. Puey said services will easily convert bitcoin to dollars with a fee, or people can buy gift cards with them. He said he sees a future where that's no longer needed.

"It'll be bitcoin to eggs and bitcoin to chickens and bitcoin to whatever commodity you wish to purchase," Puey said.

For now, most Americans will only take coins that they can hold in their hand.